1. Technical Field This application relates generally to a power converter which is equipped with a discharging resistor and designed to enhance the stability in operation thereof.
2. Background Art
Power converters are known which work to perform power conversion between DC power and AC power and are equipped with a smoothing capacitor and a discharging resistor for releasing electric charge stored in the smoothing capacitor. For instance, Japanese Patent First Publication Nos. 2010-124523 and 11-235043 teach such a type of power converter. FIG. 13 illustrates an example of a conventional power converter.
The power converter 9 consists of a plurality of semiconductor modules 90 in which semiconductor devices are installed. Each of the semiconductor modules 90 includes control terminals 99 and power terminals 920. The control terminals 99 are joined to a control circuit board 93. The control circuit board 93 has fabricated thereon electronic parts working to control switching operations of the semiconductor modules 90.
A smoothing capacitor 95 is coupled to the power terminals 920 of the semiconductor modules 90 to smooth DC voltage. A discharging resistor 96 is connected in parallel to the smoothing capacitor 95.
The discharging resistor 96 is mounted on the control circuit board, thereby eliminating a space required to secure the discharge resistor 96 directly to a housing or casing 97 to reduce the overall size of the power converter 9.
Upon turning on of the power converter 9, electric charge is stored in the smoothing capacitor 95. After the power converter 9 is turned off, the electric charge is released from the smoothing capacitor 95 through the discharging resistor 96, thereby lowering the voltage at the smoothing capacitor in a decreased time to minimize the risk of electrical shock.
Upon discharging of the smoothing capacitor 95, the electric current flows through the discharging resistor 96 mounted on the control circuit board 93, heating it. This may cause a portion of the circuit on the control circuit board which is susceptible to heat to be thermally damaged by the discharging resistor 96, which leads to a malfunction of the circuit on the control circuit board 93.